This is a remix of the awesome inserts created by Hamspiced here:
https://www.thingiverse.com/thing:6504138/

This insert is a version of these for the Seeed Studio XIAO NRF52480 for 150mm x 100mm project boxes that have the grid inserts.
My personal favorite is the one here, but any in this dimensions should work:
https://www.amazon.com/dp/B07KXRW62F

Add in your own battery to the plate and you're good to go.

Also, because the charge controller on the XIAO kind of sucks, I included a version with a holder for a solar charge controller. This holder has a cut out at the bottom for the charge controller to "breath" so it doesn't overheat and holes for zip ties along the right side to hold a battery. For the charge controller variant, I used a TP4056 USB C charge controller.